In recent years, the application of a curvilinear motion rolling guide unit to sliding sections of various apparatus, such as curvilinear reciprocating motion mechanisms or the like of industrial robots, for example, has been expanding. Usually, for smooth rolling of rolling elements on a circulation passage and for good lubrication to the rolling elements, lubricant is periodically supplied from a lubrication port. However, in view of energy savings, implementation of simple structure and low cost for the apparatus, and a reduction of running cost and equipment maintenance cost, the apparatus has been required to be of maintenance-free design. In this connection, curvilinear motion rolling guide units incorporated in the apparatus have been greatly desired to implement maintenance-free design in which lubricant is not supplied in use, or to minimize the amount of use of lubricant.
Conventionally, Japanese Patent Application Laid-Open No. S62-101914, for example, discloses a swing bearing, as a curvilinear motion rolling guide unit, used to support various swing sections of industrial robots, for example. The swing bearing is composed of a raceway member having loaded-ball grooves formed in inner and outer curved surfaces, respectively, each having a fixed radius of curvature; a bearing body having loaded-ball grooves whose radiuses of curvature are suited for the loaded-ball grooves of the raceway member and which are formed in inner surfaces of two leg portions, respectively; and unloaded-ball circulation means. Mutually opposed J-shaped tube members are used as the unloaded-ball circulation means of a bearing assembly. Attachment covers for the tube members are provided at side sections of the bearing body. Each of the tube members is in a halved structure for easy forming work and assembling work.
Japanese Patent Application Laid-Open No. 2013-29116, for example, discloses a curvilinear motion guide device, as a curvilinear motion rolling guide unit, configured to allow movement of a moving member along a direction in which a curvilinearly extending raceway member extends. The curvilinear motion guide device includes the curvilinearly extending raceway member; the moving member which can move along the extending direction of the raceway member through rolling elements disposed between the moving member and the raceway member; and an infinite circulation passage formed in the moving member and allowing the rolling elements to roll therein. The infinite circulation passage is formed in such a manner as to be surrounded by a loaded-rolling-element rolling surface of the moving member and a rolling-element rolling surface of the raceway member disposed opposite the loaded-rolling-element rolling surface. The infinite circulation passage includes a loaded-rolling-element rolling passage extending curvilinearly along the extending direction of the passage member and a rolling-element return passage formed in the moving member and extending curvilinearly along the loaded-rolling-element rolling passage.
The applicant of the present invention developed a rectilinear motion guide unit in which exterior pipes used to form the return passages are disposed in outer grooves formed in wings, respectively, of a casing, and filed a patent application (see, for example, Japanese Patent Application Laid-Open No. 2013-15189) for the rectilinear motion guide unit. The rectilinear motion guide unit implements a compact, simple slider structure through employment of a unitary construction of the exterior pipes and spacers of end caps and resultant facilitation of assembling work of the slider, and thus is manufactured at low cost. The slider includes a casing composed of a flat plate-like upper section and the wings extending downward from the upper section; a pair of the end caps fixedly attached to end surfaces, respectively, of the casing; a pair of the exterior pipes disposed on outer side surfaces of the wings, respectively, of the casing and provided at the end caps; and a pair of interior pipes fitted in the respective exterior pipes and whose holes define the return passages.
The applicant of the present invention also filed a patent application for a curvilinear motion rolling guide unit in which a slider sliding on a raceway rail extending curvilinearly at a fixed radius of curvature has a well-balanced, small-sized structure and allows use of end caps of the same specifications irrespective of the specifications of the slider (see, for example, Japanese Patent Application Laid-Open No. 2001-241437). The curvilinear motion rolling guide unit is formed such that each of opposite end surfaces of a casing of the slider is in a vertical plane which passes through the center of curvature of the raceway rail and is perpendicular to the raceway rail, irrespective of the length of the casing. Common specifications can be imparted to the end caps in which direction changing passages are formed. Since linear return passages are disposed toward the inside of the casing, the casing does not have a radially excess width, whereby the casing can have a radially well-balanced, small-sized structure.
However, in the above-mentioned swing bearing, since the slider is formed into a rectangular shape, and the return passages are formed linearly, the width of the slider increases accordingly; thus, the swing bearing fails to implement a compact structure. Also, since a lubrication component is not provided, periodic lubrication is required. In the above-mentioned curvilinear motion guide device, the slider is formed into a fan shape; however, since a lubrication component is not provided as in the case of the above swing bearing, periodic lubrication is required.